This invention relates to optical temperature sensors and optrodes with optical temperature compensation.
The determination of chemical parameters, eg, of the partial pressure of gases such as oxygen, carbon dioxide and ammonia, the pH, the concentration of dissolved ionic compounds, etc. by means of optical-chemical sensors (optrodes) is known. Like electrochemical sensors, these optrodes have a temperature-dependent response. Use of these sensors consequently requires simultaneous measurement of the specimen temperature and of the temperature in the chemically sensitive layer. For this purpose, use is made almost exclusively at present of electrical temperature sensors. This means, however, that a major advantage of optrodes, namely that they can be used in electromagnetic fields, is lost. In addition, combining an optical-chemical sensor with an electrical temperature sensor often makes it more expensive to manufacture the optrode. There is thus less advantage to be seen in using the optrode as a cheap, disposable sensor. Moreover, temperature compensation of measurements made with electrical temperature sensors is in many cases not feasible anyway.
So far, only few experiments have been described in which temperature compensation is achieved using optical means. The Israeli patent application IL-A-96 100 describes a process for determining a gas, a vapor, or a gas dissolved in a liquid specimen by means of a two-sensor system. The first sensor is a chemical sensor which contains a fluorescent reagent and is in contact with the measuring medium. The second sensor is a reference sensor which contains the same fluorescent reagent in a form isolated from the measuring medium.
U.S. Pat. No. 5,115,811 discloses a fiberoptic sensor for determining a parameter in a measuring medium. It contains a chemical sensor with a colorant composition whose optical properties correlate with the changes in the parameter to be determined. The sensor is coupled with a light source and with a device for measuring the light at three different wavelengths. The first wavelength is selected such that the optical properties of the colorant remain more or less constant despite changes in the parameter under analysis. The second and third wavelengths are selected such that the optical properties of the colorant vary in correlation with changes in the parameter under analysis and also as a function of the temperature. The light measured at the three wavelengths is evaluated to determine the temperature of the measuring medium, necessary in order to obtain temperature compensation for the parameter being determined.
Both the above-described procedures have the disadvantage that they only compensate for certain temperature effects, since they do not provide the means for absolute temperature measurements.
Austrian patent AT-B-393 326 relates to a method for the quantitative determination of at least one parameter in a liquid or gaseous specimen, with the fluorescent radiation emitted after excitation being measured in an indicator substance which is in direct or diffusion contact with the specimen, the change in a first parameter under analysis being obtained from the change in the ratio of two intensities determined at different wavelengths of the excitation or emission spectrum of the indicator substance and the change in a second parameter being obtained from the change in the afterglow time of the fluorescent radiation from the same indicator substance, selected from the group of aromatic hydrocarbons, aromatic heterocyclics and metallo-organic complexes. The disadvantage of this method consists in that, due to the use of just one indicator substance for determining two parameters, no independent measuring signals can be obtained for these two parameters. Consequently, no spectral separation is possible, nor is it possible to simultaneously measure the afterglow time for two parameters. Due to the fact that the indicator of the AT-B-393 326 is in contact with the measuring medium, interactions between components of the medium and the indicator can moreover lead to inaccurate results during a temperature determination. In practice, these disadvantages mean that the sensor described in the AT-B-393 326 is only of very limited use for the temperature-compensated measurement of chemical parameters.
The DE-C-32 13 183 relates to an arrangement for the optical determination of physical and chemical parameters of a system under test, with a photometric device having at least one radiation source, a monochromatic filter, an opto-receiver and a display device, and at least one indicator chamber which is separated from the system under test by a semi-permeable membrane and which contains an indicator that responds to the physical or chemical parameters under analysis by changing its spectral properties; the absorption capacity and the film thickness of the indicator are selected such that the side of the membrane in contact with the system under test is not reached by the test light. The arrangement can also include nano capsules as secondary indicator chambers, which contain indicators that respond to one or more additional physical or chemical properties with a change in their spectral characteristics. Liquid crystals which change color as the temperature changes are cited as examples of indicators in the nano capsules. The DE-C-32 13 183 does not disclose the use of indicators which are inert towards the medium and which have a temperature-dependent afterglow time and/or intensity of the luminescence.
There are some optical temperature sensors based on the temperature-dependent afterglow time of crystals or phosphors. These optical temperature sensors, however, have so far not been used in conjunction with chemical optrodes.
The use of luminescent metallo-organic compounds--eg, ruthenium complexes with heterocyclic nitrogen ligands--as oxygen indicators for optrodes is known (cf. eg, Wolfbeis et al., Mikrochim. Akta (Vienna) 1986, III, 359-366; Bacon and Demas, Anal. Chem. 1987, 59, 2780-2785; Carraway et al., Anal. Chem. 1991, 63, 337-342; McGraith et al., Analyst 1993, 118, 385-388). The basic idea of using luminescent ruthenium complexes as temperature indicators has already been suggested by Demas et al.(Proc. SPIE 1992, vol. 1796, 71-75). However, this publication does not contain any indication that it is possible to reference the temperature influence of optrodes in this way.
One of the objectives of this invention was to overcome--at least partially--the disadvantages of the methods known from prior art for measuring temperature and for the temperature-compensated determination of chemical parameters. In particular, the invention was intended to provide a method for the temperature-compensated determination of parameters which is easy to carry out and is not affected by strong electromagnetic fields.
The object of the invention is established by means of a device for the temperature-compensated determination of chemical parameters, comprising:
an optical temperature sensor which contains a temperature indicator that has a temperature-dependent afterglow time and/or intensity of the luminescence and does not react with the surrounding medium; PA1 a chemical sensor which contains an indicator that is sensitive to a chemical parameter; PA1 means for stimulating the temperature indicator and the chemical indicator to luminesce; means for measuring the luminescence of the temperature indicator and of the chemical indicator; PA1 means for establishing an optical connection between indicator, excitation device and measuring equipment and PA1 means for detecting luminescent radiation.